Current tumour treatments are limited by the existence of highly malignant cell types, which intrinsically fail to respond to conventional treatments (gliomas, sarcomas, etc.), or by the onset of selective advantages, which promote the selection and consequent proliferation of resistant tumour clones during treatment (Woodhouse, E. C., et al., Cancer 80:1529-1537, 1997). Conventional treatments are mainly designed to inhibit the growth of the tumour rather than preventing its metastatic spread, which is still the main cause of treatment failures (Shevde L A et al. Cancer Lett, 198:1-20, 2003).
The general characteristic of current tumour treatments is the use of highly cytotoxic compounds which, although they act selectively on malignant cells, inevitably have devastating systemic effects on the body. The result is that current treatments generally involve very high social, human and financial costs.
This overall picture demonstrates that: a) there is a pressing need to develop effective treatments for currently untreatable tumours; b) there is a strong need to reduce the side effects which make patients' quality of life unacceptable when they are treated with current anti-tumour drugs, and can even cause death in debilitated patients; c) the efficacy of treatments needs to be improved by using drugs that interfere both with the growth process and with the metastatic spread of the tumour; d) the cost of tumour treatments needs to be made more acceptable.
It was recently reported that the numerous biological actions of the peptide Metastin, of human and murine derivation (WO 00/24890, WO 01/75104, WO 02/85399) include an effect in the prevention or treatment of cancer. WO 06/001499, which relates to Metastin and its derivatives, claims a very broad series of compounds, estimated at over 1010 different structures, containing 4 to 54 amino acid residues, natural and non-natural, for which a very wide variety of biological activity is reported, such as inhibition of metastatic spread and growth of tumours, control of the pancreatic function and prevention of acute and chronic pancreatitis, control of the placental function and use in the treatment of foetal hypoplasia, abnormal glucose metabolism, abnormalities in the lipid metabolism, infertility, endometriosis, premature puberty, Alzheimer's disease, disorders affecting the cognitive sphere, obesity, hyperlipidaemia, diabetes mellitus type II, hyperglycaemia, hypertension, diabetic neuropathies, diabetic nephropathies, diabetic retinopathies, oedema, urinary disorders, insulin resistance, unstable diabetes, fatty atrophy, insulin allergies, atherosclerosis, thrombotic disorders, lipotoxicity, and use in treatments to improve the function of the gonads and stimulate ovulation. The simultaneous existence of such different biological actions for each of these compounds certainly represents a major limitation, not an advantage, with a view to the therapeutic application of this class of molecules. This wide variety of biological functions is closely associated with the interaction of Metastin and its derivatives with the specific cell receptor GPR54, also known as Kiss-1R, Kisspeptins receptor, Metastin receptor, hypogonadotropin 1 or hOT7T175 (Ohtaki T., et al., Nature 411:613-617, 2001; Clements M. K., et al., Biochem. Biophys. Res. Commun. 284:1189-1193, 2001; Muir A. I., et al., J. Biol. Chem. 276:28969-28975; 2001; Kotani M., et al., J. Biol. Chem. 276:34631-34636, 2001; Seminara S. B., et al., N. Engl. J. Med. 349:1614-1627, 2003; Grimwood J., et al., Nature 428:529-535, 2004; Colledge W. H., Trends Endocrinol. Metab. 15:448-453, 2004; Hori A., et al., Biochem. Biophys. Res. Commun. 286:958-963, 2001; Janneau J.-L., et al., J. Clin. Endocrinol. Metab. 87:5336-5339, 2002; Ringel M. D., et al., J. Clin. Endocrinol. Metab. 87:2399-2399, 2002; de Roux N., et al., Proc. Natl. Acad. Sci. U.S.A. 100:10972-10976, 2003; Ikeguchi M., et al., J. Cancer Res. Clin. Oncol. 129:531-535, 2003; Ikeguchi M., et al., Clin. Cancer Res. 10:1379-1383, 2004; Bilban M., et al., J. Cell Sci. 117:1319-1328, 2004; Becker J. A. J., et al., Biochem. Biophys. Res. Commun. 326:677-686, 2005; Semple R. K., et al., J. Clin. Endocrinol. Metab. 90:1849-1855, 2005).
As regards the anti-tumoral activity of Metastin and its derivatives, WO 06/001499 reports a modest activity, limited to experimental animal models, at the dose of 70-140 μg/kg, which reduces the tumour mass by not more than 20%. It has also been demonstrated that long-term administration of Kisspeptin-54, one of the analogues of Metastin, causes the adverse effect of atrophy of the gonads in the rat (E. L. Thomson et al., Am. J. Physiol. Endocrinol. Metab. 291, 1074-1082, 2006).